The invention relates to an expansible anchor for anchoring in a hole drilled in a component, especially a concrete part.
An expansible anchor for anchoring in a hole drilled in a concrete part is known and consists of a shank having means for fixing an article at its rear end and a reduced cross-section portion with an adjoining expander cone at its front end, and, positioned over the portion of the shank of reduced cross section, an expansible sleeve having longitudinal slits forming expansible segments and locking elements protruding beyond a diameter of the expansible sleeve and arranged on the expansible segments.
Expansible anchors of that kind are especially suitable for anchoring in hard building materials. By screwing a nut onto the threaded shank projecting beyond the component and the article to be fixed, the expander cone integrally formed with the shank is drawn into the expansible sleeve bearing against the wall of the drilled hole. The expansible sleeve is consequently expanded and becomes wedged in the drilled hole. The expansible sleeve is braced in the drilled hole by locking elements provided on it, which catch against the wall of the drilled hole.
Expansion of the expansible sleeve is normally facilitated by several longitudinal slits. The longitudinal slits form expansible segments, however a closed sleeve portion is provided at the end of the longitudinal slits. The holding force of such an expansible anchor depends very considerably on the wall thickness of the expansible sleeve, and is limited to avoid too great a cross-sectional weakening of the reduced portion receiving the expansible sleeve. If the wall thickness is inadequate and the expansible segments are therefore lacking in rigidity, the withdrawal path of the expander cone into the expansible sleeve is relatively long, and this is apparent as a loss in holding force, especially in the case of relatively large drilled holes. The same effect is also apparent when the drilled hole widens subsequently as a consequence of cracks forming. Because the expansible segments buckle behind the expander cone due to inadequate rigidity, there is a considerable loss in holding force. The known expansible anchors are therefore not suitable for use in the tensile zone in which cracks may form as a result of tensile stresses occurring in the concrete.